Before DNA base pairs can be added to a new strand what addition is required?

Before DNA base pairs can be added to a new strand what addition is required?

• A. RNA primer
• B. DNA primer
• C. Okazaki fragment
• D. Ligase

Answer: (A)

DNA polymerase can only add nucleotides to an existing 3' end, so a starting point is needed. That starting point is an RNA primer laid down by primase. The primer provides a free 3' hydroxyl for DNA polymerase to attach the first DNA nucleotides and begin synthesis. Once elongation begins, the primer is later removed and replaced with DNA, and any gaps are sealed by ligase. While RNA primers are also used to start each Okazaki fragment on the lagging strand, the essential addition required to start a new strand is the RNA primer.

DNA polymerase can only add nucleotides to an existing 3' end, so a starting point is needed. That starting point is an RNA primer laid down by primase. The primer provides a free 3' hydroxyl for DNA polymerase to attach the first DNA nucleotides and begin synthesis. Once elongation begins, the primer is later removed and replaced with DNA, and any gaps are sealed by ligase. While RNA primers are also used to start each Okazaki fragment on the lagging strand, the essential addition required to start a new strand is the RNA primer.